The third generation partnership projects (3GPP) initiated a long term evolution (LTE) of the 3rd generation (3G) in 2005, and better support for increasing service requirements of operators and users is provided through evolved universal terrestrial radio access (E-UTRA) and an evolved universal terrestrial radio access network (E-UTRAN).
In an LTE system, downlink communication services can be divided into two categories, that is, a unicast service and a multimedia broadcast multicast service (MBMS). The unicast service refers to a point-to-point service in which one data source sends data to one user equipment, and the MBMS refers to a point-to-multipoint service in which one data source sends data to multiple user equipment. The introduction of the MBMS is to realize resource sharing on a network; the network includes a core network and a radio access network and serves the maximum multimedia user equipment having the same requirements by using the minimum of resources. In the radio access network, the MBMS can realize the multicast and broadcast of messages with plain texts at a low rate and realize the multicast and broadcast of multimedia services at a higher rate on a common transport channel and a common radio bearer.
For the MBMS, the specification 25.814 of the 3GPP supports two cell transmission modes, one of which is a multi-cell transmission mode, that is, multiple cells simultaneously send the MBMS with the same frequency resource, and the other of which is a single-cell transmission mode, that is, a single cell sends the MBMS without considering the transmission of other cells.
Data transmission modes of the MBMS include two modes, one of which is a mixed carrier (MC) mode, that is, the MBMS and the unicast service share the same carrier to transmit data, and the other of which is a dedicated carrier (DC) mode, that is, the MBMS itself uses one carrier to transmit data. In the case of the MC mode, the MBMS and the unicast service are in time division multiplexing, and the two services are subframe-level time division multiplexing decided by a 3GPP meeting, that is, each service occupies at least one subframe. If a base station does not send any signaling to inform the usage of each subframe, unicast service user equipment and MBMS user equipment will attempt to read their own service information through the entire transmission time, thus wasting electric energy of the user equipment. If one bit of information is set for each subframe to indicate the usage, for example, one bit has two states, 0 and 1, corresponding to the two services respectively, then the required information amount is very large.
In addition, an orthogonal frequency division multiplexing (OFDM) technology is employed in the downlink of LTE. The OFDM technology divides a given channel into multiple orthogonal subchannels in a frequency domain, and allows subcarrier spectra to be partially overlapped. As long as mutual orthogonality is met among the subcarriers, data signals can be obtained. In the operation of an OFDM system, symbols are firstly subject to serial/parallel conversion to form multiple low-rate sub-data streams, each data stream occupies one subcarrier, the mapping from the sub-data streams to the subcarriers can be achieved through an inverse discrete Fourier transform (IDFT) or an inverse fast Fourier transform (IFFT), and a cyclic prefix (CP) as a guard interval is applied, which greatly reduces or even eliminates inter-symbol interference, and ensures orthogonality among various channels, thus greatly reducing inter-channel interference.
In the subframe which sends the unicast service or a single-cell transmission MBMS, the length of the CP only needs to meet the requirements of the serving cell. In the subframe of a multi-cell transmission MBMS, the signal needs to pass through a longer transmission path, in which case a longer CP is required to overcome inter-symbol interference and user equipment can successfully demodulate a subframe only after knowing the length of the CP of the subframe.
To sum up, the base station can not effectively inform the transmission time of various services and the length of the CP of each subframe in the case of time division multiplexing for multiple services in the prior art.